A Long-Term Evolution (LTE) system offers high peak data rates, low latency, improved system capacity, and low operating cost resulting from simple network architecture. An LTE system also provides seamless integration to older wireless network, such as GSM, CDMA and Universal Mobile Telecommunication System (UMTS). In LTE systems, an evolved universal terrestrial radio access network (E-UTRAN) includes a plurality of evolved Node-Bs (eNodeBs or eNBs) communicating with a plurality of mobile stations, referred as user equipments (UEs). Enhancements to LTE systems are considered so that they can meet or exceed International Mobile Telecommunications Advanced (IMT-Advanced) fourth generation (4G) standard.
The signal bandwidth for next generation 5G new radio (NR) system is estimated to increase to up to hundreds of MHz for below 6 GHz bands and even to values of GHz in case of millimeter wave bands. Furthermore, the NR peak rate requirement can be up to 20 Gbps, which is more than ten times of LTE. It is therefore expected that 5G NR system needs to support dramatically larger transport block (TB) sizes as compared to LTE, which result in a much more code block (CB) segments per TB. Three main applications in 5G NR system include enhanced Mobile Broadband (eMBB), Ultra-Reliable Low Latency Communications (URLLC), and massive Machine-Type Communication (MTC) under milli-meter wave technology, small cell access, and unlicensed spectrum transmission. Multiplexing of eMBB & URLLC within a carrier is also supported.
A technique referred to as Hybrid Automatic Repeat ReQuest (HARQ) is employed for error detection and correction. HARQ is a combination of forward error correction (FEC) and Automatic Repeat ReQuest (ARQ). It uses error detection to detect uncorrectable errors. The packets in error are discarded and the receiver requests retransmission of corrupted packets. In a standard ARQ, error detection bits are added to data to be transmitted. In Hybrid ARQ, error correction bits are also added. When the receiver receives a data transmission, the receiver uses the error detection bits to determine if data has been lost. If it has, then the receiver may be able to use the error correction bits to recover the lost data. If the receiver is not able to recover the lost data using the error correction bits, then the receiver may use a second transmission of additional data (including more error correction information) to recover the data. Error correction can be performed by combining information from the initial transmission with additional information from one or more subsequent retransmissions.
HARQ consists of multiple HARQ processes with each operation on a single transport block (TB). The transmitter stops and waits for an acknowledgement (ACK) from the receiver, called HARQ-ACK, after each transmission of TB. The HARQ-ACK indicates whether the TB is correctly received or not. In 3GPP 5G NR, data services with low latency becomes a key differentiation from 4G LTE. From a latency perspective, the time between the reception of data and transmission of HARQ-ACK should be as short as possible. However, an unnecessarily short time would increase the demand on the processing capability. To achieve low latency, UE throughput may be sacrificed for a tradeoff due to UE hardware limitation and power consumption. A single HARQ operation scheme is sought to support the tradeoff between low-latency and high-performance.